Question 1

Which of the following nutrients is most likely to limit plant growth if deficient, and why?

Accepted Answer

Nitrogen, because it is a macronutrient and often a limiting nutrient in soils.

Question 2

A plant growing in soil with a high proportion of clay is likely to experience which of the following problems?

Accepted Answer

Difficulty in root penetration and poor oxygen availability.

Question 3

Which soil horizon contains the highest concentration of humus and microorganisms?

Accepted Answer

A horizon (topsoil)

Question 4

Why are young leaves typically the first to show symptoms of immobile nutrient deficiencies?

Accepted Answer

Immobile nutrients cannot be transported from older to younger tissues.

Question 5

Which process allows plants to extract cations such as $$\mathrm{Mg$$^{2+}$$}$$ and $$\mathrm{Ca$$^{2+}$$}$$ from soil particles?

Accepted Answer

Cation exchange, where protons replace cations on soil particles.

Question 6

A farmer notices yellowing between the veins of older leaves. Which nutrient is most likely deficient?

Accepted Answer

Magnesium ($$\mathrm{Mg})$$

Question 7

Which of the following best describes the role of proton pumps in plant root cells?

Accepted Answer

They create an electrochemical gradient that drives the uptake of ions.

Question 8

Why is nitrogen fixation critical for plant nutrition, and which enzyme complex is responsible?

Accepted Answer

It converts $$\mathrm{N_2$} to$$ $$\mathrm{NH_3$}$$, and is catalyzed by nitrogenase.

Question 9

Which of the following is a mutualistic relationship that enhances phosphorus uptake in most terrestrial plants?

Accepted Answer

Mycorrhizae, where fungal hyphae increase root surface area.

Question 10

A soil sample is found to have 40% sand, 40% silt, and 20% clay. According to the soil texture triangle, what is the soil type?

Accepted Answer

Loam

Question 11

Which of the following best explains why phosphate ($$\mathrm{PO_4$^{3-}}) is $$often a limiting nutrient in soils?

Accepted Answer

It forms insoluble complexes with iron and calcium, making it less available.

Question 12

Which adaptation allows legumes to thrive in nitrogen-poor soils?

Accepted Answer

Formation of root nodules housing nitrogen-fixing rhizobia.

Question 13

What is the primary function of leghemoglobin in root nodules?

Accepted Answer

To bind oxygen and protect nitrogenase from inactivation.

Question 14

Which of the following is an example of active exclusion of toxic ions in plant cells?

Accepted Answer

Na+/H+ antiporters at the tonoplast remove sodium from the cytoplasm.

Question 15

A plant growing in alkaline soil with high $$\mathrm{$$CaCO_3$$}$$ content is likely to experience which of the following?

Accepted Answer

Reduced availability of iron and phosphate due to precipitation.

Question 16

Which of the following best describes the movement of water and nutrients from the soil into the xylem?

Accepted Answer

They move through the apoplast until the Casparian strip, then enter the symplast via endodermal cells.

Question 17

Which of the following is a real-world consequence of soil erosion?

Accepted Answer

Loss of topsoil, leading to decreased agricultural productivity.

Question 18

Which of the following best explains why humus is important for soil fertility?

Accepted Answer

It increases cation exchange capacity and water retention.

Question 19

Which of the following is a function of metallothioneins in plant cells?

Accepted Answer

Binding toxic metals to prevent poisoning.

Question 20

Which of the following best describes the role of root hairs in nutrient uptake?

Accepted Answer

They increase the surface area for absorption of water and minerals.

Plant Nutrition: Soil, Nutrients, and Symbiotic Relationships

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